1995 C280 Dash Lights

Recently the dashboard light on the left side of the speedometer on my 1995 C280 went out and I thought the bulb needed replacement. Before I could get it in for servicing, the light came back on. Since then the bulb has gone off and come on again several times. Now, the bulb on the right side of the speedometer has started the same thing sometimes coming on sometimes going out. It never does this while the car is running, it is always just a guess whenever you start the car whether the bulb to the left of the speedometer will light, the right one will light, both will light or neither will light. Has anyone else experienced this? Is there a common ground point that may have loosened or corroded?